Restrict TMPDIR etc. changes to install, post_install and test

See discussion in Homebrew/brew#800.

Library/Homebrew/build.rb

@@ -103,6 +103,11 @@ class Build
       end
     end
 
+    old_tmpdir = ENV["TMPDIR"]
+    old_temp = ENV["TEMP"]
+    old_tmp = ENV["TMP"]
+    ENV["TMPDIR"] = ENV["TEMP"] = ENV["TMP"] = HOMEBREW_TEMP
+
     formula.extend(Debrew::Formula) if ARGV.debug?
 
     formula.brew do |_formula, staging|
@@ -139,6 +144,10 @@ class Build
         formula.prefix.install_metafiles formula.libexec if formula.libexec.exist?
       end
     end
+  ensure
+    ENV["TMPDIR"] = old_tmpdir
+    ENV["TEMP"] = old_temp
+    ENV["TMP"] = old_tmp
   end
 
   def detect_stdlibs(compiler)

Library/Homebrew/config.rb

@@ -35,11 +35,6 @@ HOMEBREW_LOGS = Pathname.new(ENV["HOMEBREW_LOGS"] || "~/Library/Logs/Homebrew/")
 # Must use /tmp instead of $TMPDIR because long paths break Unix domain sockets
 HOMEBREW_TEMP = Pathname.new(ENV.fetch("HOMEBREW_TEMP", "/tmp"))
 
-# Set common tmpdir environment variables to HOMEBREW_TEMP
-ENV["TMPDIR"] = HOMEBREW_TEMP
-ENV["TEMP"] = HOMEBREW_TEMP
-ENV["TMP"] = HOMEBREW_TEMP
-
 unless defined? HOMEBREW_LIBRARY_PATH
   # Root of the Homebrew code base
   HOMEBREW_LIBRARY_PATH = Pathname.new(__FILE__).realpath.parent

Library/Homebrew/formula.rb

@@ -888,11 +888,18 @@ class Formula
   def run_post_install
     build = self.build
     self.build = Tab.for_formula(self)
+    old_tmpdir = ENV["TMPDIR"]
+    old_temp = ENV["TEMP"]
+    old_tmp = ENV["TMP"]
+    ENV["TMPDIR"] = ENV["TEMP"] = ENV["TMP"] = HOMEBREW_TEMP
     with_logging("post_install") do
       post_install
     end
   ensure
     self.build = build
+    ENV["TMPDIR"] = old_tmpdir
+    ENV["TEMP"] = old_temp
+    ENV["TMP"] = old_tmp
   end
 
   # Tell the user about any caveats regarding this package.
@@ -1411,7 +1418,11 @@ class Formula
   def run_test
     old_home = ENV["HOME"]
     old_curl_home = ENV["CURL_HOME"]
+    old_tmpdir = ENV["TMPDIR"]
+    old_temp = ENV["TEMP"]
+    old_tmp = ENV["TMP"]
     ENV["CURL_HOME"] = old_curl_home || old_home
+    ENV["TMPDIR"] = ENV["TEMP"] = ENV["TMP"] = HOMEBREW_TEMP
     mktemp("#{name}-test") do |staging|
       staging.retain! if ARGV.keep_tmp?
       @testpath = staging.tmpdir
@@ -1430,6 +1441,9 @@ class Formula
     @testpath = nil
     ENV["HOME"] = old_home
     ENV["CURL_HOME"] = old_curl_home
+    ENV["TMPDIR"] = old_tmpdir
+    ENV["TEMP"] = old_temp
+    ENV["TMP"] = old_tmp
   end
 
   # @private